The present invention relates to improvements in combustion tools, such as the type used for driving fasteners into work pieces. More specifically, the present invention relates to high-powered combustion tools.
A suitable combustion-powered tool assembly is described in commonly assigned patents to Nikolich U.S. Pat. No. 5,197,646, and U.S. Pat. Nos. 32,452, 4,552,162, 4,483,473, 4,483,474, 4,403,722, and 5,263,439, which are incorporated by reference. Such fastener-driving tools are available commercially from ITW-Paslode (a division of Illinois Tool Works, Inc.) of Vernon Hills, Ill., under its IMPULSE trademark.
Such tools incorporate a generally pistol-shaped tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A powerful, battery-powered electronic power distribution unit produces the spark for ignition, and a fan located in the combustion chamber provides for both an efficient combustion within the chamber, and facilitates scavenging, including the exhaust of combustion by-products. The engine includes a reciprocating piston with an elongate, rigid driver blade disposed within a cylinder body.
A valve sleeve is axially reciprocable about the cylinder and, through a probe assembly linkage, moves to close the combustion chamber when a work contact element at the end of the probe assembly is pressed against a workpiece. This pressing action also triggers a fuel metering valve to introduce a specified volume of fuel into the closed combustion chamber.
Upon the pulling of a trigger switch, which causes the ignition of a charge of gas in the combustion chamber of the engine, the piston and driver blade are shot downward to impact a positioned fastener and drive it into the workpiece. The piston then returns to its original, or “ready” position through differential gas pressures within the cylinder. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
There is a general interest by designers of such combustion tools to increase combustion efficiency. This has resulted in tools with greater power, generated by a more powerful combustion event in the combustion chamber. One disadvantage of conventional combustion tool assemblies is that, as the tool is operated, significant loads are applied to the workpiece contacting element and transmitted throughout the tool assembly. In particular, as the piston and attached driver blade drive the fastener and reach the bottom of the piston stroke, significant impact forces are generated. These forces are transmitted through the cylinder to the movable valve sleeve, which is connected through a linkage to the workpiece contact element also referred to as the probe assembly. Impact forces are particularly felt at contact points between the cylinder and the valve sleeve/probe assembly. As such, as combustion tools increase in power, the higher loads can lead to breakage of the various parts of the tool, especially the above-discussed contact points between the probe assembly and lower portion of the valve sleeve. Tests have shown that during operation of a typical combustion tool, the piston speed tops about ninety miles per hour is reduced to zero miles per hour at impact. Such repeated impacts have in some cases reduced tool operation life due to premature breakage of components.
Another disadvantage of conventional combustion tool assemblies with higher-powered combustion is that a high driving velocity of the piston can also lead to a higher return velocity of the piston after driving the fastener into the workpiece. The shock from abruptly stopping the piston at the top of the cylinder, as the upper probe assembly contacts the stop tabs on the cylinder or valve sleeve, can cause the piston to bounce back down the cylinder away from the proper firing position. A movement away from the proper firing position can unintentionally increase the volume of the combustion chamber and lead to misfires of the tool.
Still another factor in the use of combustion tools is that there is constantly a need for lighter and smaller tools. Nikolich U.S. Pat. No. 5,197,646, listed above, describes a suitable assembly for shortening the overall length of a combustion-powered tool; however, there is a need for continual improvement in the overall weight of the tool.
Accordingly, there is a need for an improved combustion-powered tool design that reduces the load forces transmitted to the valve sleeve and probe assembly. In addition, there is a need for an improved combustion-powered tool that is less susceptible to a component failure through combustion-generated impact forces.